1. Field of the Invention
The present invention relates to a method of milking an animal, in which the animal's teats are applied in teatcup liners with tubular walls. The interior of each teatcup liner under the teat is exposed to an underpressure for extracting milk from the teat, while the wall of the teatcup liner is exposed to a cyclicly varying pressure difference between the interior of the teatcup liner under the teat and the outside of the teatcup liner, so that the teatcup liner cyclicly moves towards an open and a closed position. During an initial phase of the milking, when the milk flow is non-existent or relatively small, said pressure difference is varied such that the teatcup liners are cyclicly partly opened. During a main phase of the milking, when the milk flow is relatively large, said pressure difference is varied so that the teatcup liner is cyclicly open at least substantially completely. At least one milking variable is monitored during said initial phase, the initial phase being ended and the main phase being started when said milking variable reaches a predetermined value.
2. Description of the Prior Art
Such a milking method is known from U.S. Pat. No. 4,391,221 and intends to prevent the teatcup liners from crawling upwards on the teats, when the milk flow still is relatively small and the teats as a consequence thereof are relatively slack. Thus, it is ensured that the frictional engagement between the teatcup liners and slack teats are kept intact by not opening the teatcup liners completely during said initial phase of the milking.
A teatcup liner which has crawled upwards on its teat may throttle or even completely close the passage between the udder cistern and the teat, which results in that the milk flow from the teat is reduced or ceases.
Teatcup liner crawling can therefore result in a decreased milk yield and/or prolonged milking time. It would be possible to remedy an occurred case of teatcup liner crawling by first completely detach the teatcup liner in question from its teat and then reattach it on the teat. However, in practice it is difficult to discover teatcup liner crawlings, and consequently, it is important that these as much as possible are prevented from occurring at all.
By means of the known milking method according to U.S. Pat. No. 4,391,221 the initial phase of the milking is ended in response to the lapse of a predetermined time period, which can be chosen in the interval of 40-90 seconds, counted from the beginning of the initial phase. However, for for instance cows the time each cow will need to give such a relatively large milk flow which results in distended teats and thereby a good engagement with fully opening teatcup liners is very individual. Thus, some cows may give a large milk flow already after a few seconds of the initial phase, while other cows will give a large milk flow first after about a minute of the initial phase. Therefore, the known milking method has the disadvantage that some cows are treated during an unnecessary long initial phase, which has the consequence that the total milking time will be unnecessarily long.
Therefore it may seem to be better to control the duration of the initial phase in response to the milk flow from the teats, so that the initial phase is ended when the milk flow is large enough to indicate that the teats are extended. However, the milk flow is not a reliable indicator on how prepared a cow is for milking, since the milk flow after an initial increase again may be reduced in case the cow is not sufficiently stimulated. The reduction of the milk flow in such a case depends on that only the minor milk quantity already being in the udder cisterns is extracted, while the major milk quantity being in the alveoli of the udder still has not been released.